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ceramic resistor query

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mini-mad View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 13 March 2015 at 6:34pm
Originally posted by stevie stevie wrote:

Resistors are responsible for more faults in speaker crossovers than any other component. For the few pence that it costs, over-specify the resistors, and space them off the board.

or buy 'heatsinked' wire wounds....




Edited by mini-mad - 13 March 2015 at 6:35pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote stevie Quote  Post ReplyReply Direct Link To This Post Posted: 13 March 2015 at 7:59pm
Yes, they're great - except they're not fully heatsinked as they are. You need to add a proper heatsink to achieve the quoted power handling.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 13 March 2015 at 8:10pm
Just bolt them to an L Bracket and screw said bracket to the inside of the cab!

Jobs a goujon!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tweeter_Box Quote  Post ReplyReply Direct Link To This Post Posted: 13 March 2015 at 10:25pm
   

Cheers guys

Wanna upload some pics of progress so far but files are bigger than the limit
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mini-mad Quote  Post ReplyReply Direct Link To This Post Posted: 13 March 2015 at 10:56pm
Originally posted by Tweeter_Box Tweeter_Box wrote:

   

Cheers guys

Wanna upload some pics of progress so far but files are bigger than the limit

Chuck them in windows paint and shrink/resize to 40% of original size, then drag in the borders til its a 6inch square on ya screen... resave file under different name then upload with a foot print less then 25% of original file size.

Just remember to save it as a jpeg and your good to go!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote chickenfizz Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2015 at 12:34am
Originally posted by _djk_ _djk_ wrote:

Be aware that those ceramic resistors will have a temperature rise of 250°C over ambient at their rated power.
 
Derated to 40% of rated power they will only be slightly warmer than boiling water!
 
Also keep in mind that solder melts around 180°C.

Absolutely, this can be a problem in high power passive crossovers. I've seen a number of incidents of resistors becoming unsoldered or very badly oxidised solder joints, easily melting hotglue or cable tie mounts (bad design). Best to spread the power over a number of over-rated resistors paralleled which allows the heat more surface area to dissipate from and remote them from the PCB onto a metal plate. Or better still, go active! Seems silly to deliver all of this power to the speaker only to deliberately waste it as heat. Orrr you could retain the passive crossover but without the pad, knowing that you'd have to EQ the box to stop the horn blowing your head off, but you buy yourself some amp headroom back and don't spend it on heating up a few resistors.

Also, the resistance of a wirewound resistor will increase as it gets hot which will affect the volume of the HF and the crossover frequency, the voltage drop across it becomes greater, therefore the power dissipated by it increases too and the cycle goes on.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 24 March 2015 at 1:37pm
need to mount the resistors on a reasonably large heatsink to keep them temperature and resistance stable. I've got a few 10cm and 20cm sections of the 190AB and 193AB heatsinks from ABL if anyone is interested

http://www.abl-heatsinks.co.uk/index.php?page=extrudedresults
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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2015 at 6:23am
I had a 10w resister burn out (brake ) on one of its tails just the other day .... Surely the fact that this component has already blown tells u it's a bad idea to replace with a less powerful one :D lol ,

Probably underspecced in the first place , 15 watt is the winner here
Black to black , red to red , blue to bits ....

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Post Options Post Options   Thanks (0) Thanks(0)   Quote APW Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2015 at 3:03pm
Originally posted by matty w matty w wrote:

I had a 10w resister burn out (brake ) on one of its tails just the other day .... Surely the fact that this component has already blown tells u it's a bad idea to replace with a less powerful one :D lol ,

Probably underspecced in the first place , 15 watt is the winner here


If the leg has snapped off it’s more likely to be due to metal fatigue caused by repeated mechanical stress due to the vibration caused by the sound the speaker produces within the cab or exterior vibration caused by rough handling rather than being overpowered.

Replacing with a higher powered resistor would not make any difference to the unit’s reliability and may in fact make the reliability worse due to a change in the mechanical resonance of the component; In this case a change only a change to the means of mounting the component would increase the reliability of the unit.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote matty w Quote  Post ReplyReply Direct Link To This Post Posted: 08 May 2015 at 3:59pm
Thanks APW I appreciate the advice , my advice was for the op's post not my own situation , I replaced the resister in my crossover with the exact same component ,
The resister in my crossover blew when I was doing something stupid or experimenting shall we say , I tried wiring an additional resister in series with the midrange output on a 3 way crossover , then turned it up to maximum operating power to proof test if there would be any issues .... And there was lol , I literally watched the resister on the crossover (presumably part of an l pad on the mid output)glow and brake !

I was expecting a glow from the protection bulbs to indicate to me it was running at maximum , then I planned to back it off a little , however it wasn't the protection bulb that lit up , it was the resister :D

A cheap thing to replace so no harm done and I learnt that wiring a resister in series with an output of a crossover that already has an lpad is a bad idea :D ...   Nothing like getting involved Ay
Black to black , red to red , blue to bits ....

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